The present invention relates to a radio frequency signal output module having radio frequency power amplifier and an isolator element which is used in a transmitter or the like of a portable telephone or a mobile communication terminal.
Recently, size reduction and weight reduction in a communication apparatus such as a portable telephone or a mobile communication terminal is increasingly demanded. In accordance with this, reduction of the size, the weight, and the thickness of each component constituting such a communication apparatus, decreasing the number of components, and reduced power consumption are strongly requested.
In a communication apparatus such as a portable telephone or a mobile communication terminal, usually, an isolator element which is an irreversible directional element is connected to the output of a radio-frequency power amplifier circuit in a transmission section. This connection is performed so that the isolator element blocks a radio-frequency power reflected as a result of a state change of an antenna from reaching the radio-frequency power amplifier circuit, whereby deterioration of the radio-frequency power amplifier circuit and increase of an unwanted output are prevented from occurring.
In the conventional art, a radio-frequency power amplifier circuit is formed as a module on a dielectric substrate, and then housed in a metal case serving as a shield. By contrast, in an isolator element, a magnetic material must be enclosed by a high permeability metal because of the structure of the element. In this way, an isolator element is different in material and structure from electronic components which are formed on a usual insulator substrate, and hence produced as an independent component. Namely, an isolator element of the conventional art is housed in a metal case which is different from that of a radio-frequency power amplifier circuit.
Although a radio-frequency power amplifier circuit and an isolator element are closely related in function with each other as described above, they are treated as independent components until they are mounted into a portable telephone or a mobile communication terminal. In other words, conventionally, a radio-frequency power amplifier circuit and an isolator element are prepared as independent components, respectively, and the components are then mounted by soldering onto a motherboard configured by a dielectric multilayer substrate.
Since a radio-frequency power amplifier circuit and an isolator element are handled as independent components, it is difficult to miniaturize them. When these components are mounted on a motherboard, the thickness of the isolator element is added to that of the motherboard to increase the total height, thereby producing a problem in that the whole of the radio-frequency output stage cannot be reduced in size and thickness.
An isolator element is produced so that all ports have an input/output impedance of 50 xcexa9 which is equal to a standard transmission line impedance. A radio-frequency power amplifier circuit has an output impedance of 30 xcexa9 or less, for example, 10 xcexa9. In order to connect a radio-frequency power amplifier circuit with an isolator element, therefore, an impedance matching circuit must be disposed. Furthermore, also an APC circuit must be disposed in order to control the output of the radio-frequency power amplifier circuit. Therefore, it is required to mount chip components for constituting L and C on a motherboard, or to form L by means of a copper foil pattern on the surface of the motherboard. Also an impedance matching circuit and an APC circuit configured as described above form factors of blocking reduction in size and thickness of the radio-frequency output stage.
Furthermore, components such as a radio-frequency power amplifier circuit and an isolator element must be individually obtained, and an impedance matching circuit and an APC circuit which are used for connecting such components with each other must be separately designed. Therefore, design of a communication apparatus such as a portable telephone or a mobile communication terminal is cumbersome, and affected also by variation of individual components. As a result, there is a fear that the performance of the whole communication apparatus cannot be surely maintained.
It is an object of the invention to provide a radio frequency signal output module having a radio-frequency power amplifier and an isolator element, which radio-frequency can be largely reduced in size and thickness.
It is another object of the invention to provide a radio frequency signal output module having a radio-frequency power amplifier and an isolator element which allows a communication apparatus such as a portable telephone or a mobile communication terminal to be easily designed, and which can suppress variation of the performance of the whole communication apparatus to a minimum level.
It is a further object of the invention to provide a radio frequency signal output module having a radio-frequency power amplifier and an isolator element in which the frequency characteristics of the isolator element can be easily adjusted.
According to the invention, it is provided a radio frequency signal output module comprises: a dielectric multilayer substrate; a radio-frequency power amplifier circuit; an isolator element; an impedance matching circuit which is inserted and connected between the radio-frequency power amplifier circuit and the isolator element; and a feedback loop for controlling a gain of the radio-frequency power amplifier circuit, the radio-frequency power amplifier circuit, the isolator element, the impedance matching circuit, and the feedback loop are integrally mounted on the dielectric multilayer substrate, and the feedback loop is branched from the impedance matching circuit, and connected to the radio-frequency power amplifier circuit.
The radio-frequency power amplifier circuit, the isolator element, the impedance matching circuit, and the feedback loop are integrally mounted on the dielectric multilayer substrate, and the feedback loop is branched from the impedance matching circuit, and connected to the radio-frequency power amplifier circuit. Since the radio-frequency output stage is integrated with the dielectric multilayer substrate in this way, the radio-frequency output stage can be largely reduced in size and thickness. This integration can decrease the number of components. Since the branching portion of the feedback loop is disposed in the impedance matching circuit, moreover, the structure of the feedback loop can be simplified. As a result, the radio-frequency output stage can be further miniaturized.
When the radio frequency signal output module having a radio-frequency power amplifier and an isolator element of the invention is used as described above, it is possible to attain the following effects: (1) the mounting area of the whole radio-frequency output stage can be reduced; (2) the designer of a communication apparatus such as a portable telephone or a mobile communication terminal is not required to individually obtain components such as a radio-frequency power amplifier circuit and an isolator element and design an impedance matching circuit for connecting the components, and hence the labor for designing the communication apparatus can be reduced; and (3) variation of the performance of the whole communication apparatus can be suppressed to a minimum level.
Preferably, the impedance matching circuit is built in the dielectric multilayer substrate, or formed in and on the dielectric multilayer substrate.
Preferably, the impedance matching circuit is formed by directional coupling means having a feedback terminal which is connected to the feedback loop. In this way, the input impedance of the directional coupling means is matched with the output of the power amplifier circuit, the output impedance is matched with the input of the isolator element, and the feedback loop is obtained from the impedance matching circuit, whereby the structure can be further simplified.
Preferably, at least a part of a capacitor which is connected to at least one port of the isolator element is configured by an internal electrode which is formed in the dielectric multilayer substrate, and a surface electrode which is formed on a surface of the dielectric multilayer substrate to be opposed to the internal electrode, the surface electrode being trimmable. When such a surface electrode is disposed, the frequency characteristics of the isolator element can be easily adjusted by changing the capacitance by means of laser trimming.
Preferably, main portions (specifically, a ferrite block and a central conductor) of the isolator element are integrally insertedly disposed in a mounting portion which is formed by removing a part of the dielectric multilayer substrate. More preferably, the mounting portion is a through hole of the dielectric multilayer substrate. Since the main portions of the isolator element are integrally insertedly disposed in the mounting portion such as a through hole, the radio-frequency power amplifier circuit and the isolator element can be integrated into one unit without increasing the total height, so that the thickness can be reduced.
Preferably, the radio-frequency power amplifier circuit and the isolator element are covered by a common shield case.
Preferably, the device further comprises: a SAW (Surface Acoustic Wave) element which is mounted on the dielectric multilayer substrate, and which is connected to an input of the radio-frequency power amplifier circuit; and a matching circuit which is built in the dielectric multilayer substrate, and which matches an output impedance of the SAW element with an input impedance of the radio-frequency power amplifier circuit.